The present invention has for its object a process for the rapid prototyping by powder sintering, particularly of ceramic powder, and a device for practicing said process.
Rapid prototyping is a process which permits obtaining pieces of complicated shapes without tools and without machining, from a three-dimensional image of the piece to be made, by sintering superposed layers of powder with the help of a laser.
A first prototyping process by laser sintering of powder is described in international patent application WO 96/06881. It permits particularly obtaining pieces of polymer by sintering in liquid phase polymeric powders. In this case, the temperature level generated by the laser is relatively low because the fusion temperatures of the polymers are not high, of the order of about 100xc2x0.
So as to obtain more resistant pieces of material, it is necessary, in this case, to use a so-called lost wax molding process.
This process for making a resistant piece is long and there is obtained a relatively mediocre dimensional precision for certain applications. Thus, numerous dispersions arising from the different processes do not permit obtaining precise dimensions of the order of xc2x150 xcexcm.
A second process consists in sintering in liquid phase a mixture of powder materials, one of the materials having a relatively low melting temperature of the order of several hundreds of degrees. Here again, the temperature level generated by the laser is relatively low because of the low melting temperature of one of the materials. It should be noted that the phenomenon commonly called sintering is a sintering in liquid phase and that it is more like cementing of grains, the material of a relatively low fusion temperature being used as a binder. In this case, the piece obtained is not homogeneous and the dimensional precision is relatively mediocre. Thus, the criterion of dimensional precision is not essential in this case because the operator can easily true by machining the dimensions of the pieces thus obtained.
Another process for rapid prototyping, described in U.S. Pat. No. 5,182,170, consists in causing a powder material to react, disposed in successive layers, with a gas, by heating with the help of a laser. Thus, there can be obtained pieces from certain highly resistant ceramics thanks to chemical reactions of the nitriding or cementing type. But this process cannot be applied to all ceramics.
As can be seen, the processes of the prior art do not permit obtaining homogeneous pieces from sintered ceramic powders because the fusion temperatures of the ceramics are too high.
The devices associated with these processes comprise in general a target on which are disposed successively the layers of sintered powder, means for emplacing in layers the powder, as well as means to control the stroke of the laser. The produced piece is disposed on the upper surface of a piston which can move in a cylinder whose upper end constitutes the target.
These devices are in general used at temperatures that are not very high and do not permit obtaining pieces of precise dimensions.
However, for the production of ceramic pieces, a dimensional precision is an essential criterion because the truing of the dimensions obtained at the end of the process is possible only with the aid of a diamond tool, and remains reserved for simple point operations without involving machining.
The present invention therefore seeks to provide a process for rapid prototyping by laser sintering of any powder, and particularly ceramic powders.
It also provides the associated device, adapted to be used at high temperatures, around 900xc2x0 C., and which permits obtaining by laser sintering of powders, a piece of high dimensional precision of the order of xc2x150 xcexcm, which is to say half the precision obtained by devices of the prior art.
To this end, the invention has for its object a process for rapid prototyping by sintering in solid phase, with the help of a laser, of a powder of a mixture of powders, characterized in that it comprises the steps which consist in:
1/ obtaining a series of digitized superposed sections of an object to be produced, from a three-dimensional image of said object,
2/ spreading in the form of a fine layer the powder or the mixture of powders heated to a temperature near the sintering temperature in solid phase of said powder or said mixture of powders,
3/ increasing the density of the powder of the layer,
4/ bringing the layer to the sintering temperature by sweeping said layer with the help of a laser beam such that a sectioned portion of the powder, which corresponds to one of the digitized sections of the object to be produced, is sintered in solid phase thanks to the supplemental energy supplied by the laser,
steps 2, 3 and 4 being repeated until all the digitized superposed sections of the object to be produced are obtained.
Preferably, the powder or the mixture of the powders is heated and held at a temperature of the order of 300xc2x0 C. to 900xc2x0 C., and the layer is mechanically compacted so as to increase its density.
Preferably, the laser used is a pulsed YAG laser, and the wavelength of the emitted radiation is in the near infrared.
The invention also has for its object a device for practicing said process, characterized in that it comprises a laser having control means for the stroke, in turn controlled by a computer interface, a high temperature cell provided with heating means and a target for a laser beam, a means for layering, disposed in said cell, adapted to deposit on the target a layer of powder.
According to a preferred embodiment, it comprises compacting means, disposed in the high temperature cell, adapted to compact the layer being sintering.